In human hearing, hair cells in the cochlea respond to sound waves and produce corresponding auditory nerve impulses. These nerve impulses are then conducted to the brain and perceived as sound.
When the hair cells are severely damaged or missing, one method of restoring hearing is a cochlear implant. The cochlear implant includes an electrode that is inserted into the cochlea and directly stimulates the auditory nerves using an electrical current. This bypasses the defective hair cells and restores perception of sound to the patient.
The insertion of the electrode into the cochlea is typically performed by creating an opening in the cochlea and then inserting the electrode through the opening and into the cochlea. This insertion, when performed manually, can generate forces that are large enough to damage the sensitive tissues within the cochlea. This damage can further reduce any residual hearing capability of the patient.
If hearing can be preserved, many advantages are afforded to the patient such as 1) the possibility of combined acoustic-electric hearing for better hearing in noise and music enjoyment and 2) the preservation of sensory structures that produce homeostatic levels of various growth factors that help to support spiral ganglion cell survival.
In order to increase the probability of hearing preservation in the face of electrode insertion trauma the forces exerted during insertion should, at a minimum, not exceed the mechanical limits of the tissue residing within the inner ear. It should be pointed out that the structures responsible for hearing transduction can be irreversibly damaged by forces that are below the threshold of tactile detection during manual insertion. Therefore, in order to accomplish reliable atraumatic insertions of a cochlear implant arrays, new methods must be employed that enable the management of forces that are below human detection.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.